IPv6 allowas-in 1 doesn't work

[stcheng]

  address-family ipv6                     
    neighbor FC00::72 activate            
    maximum-paths 64                      
  exit-address-family                     
  neighbor FC00::76 remote-as 64600       
  neighbor FC00::76 description ARISTA02T1
  neighbor FC00::76 allowas-in 1          
  address-family ipv6                     
    neighbor FC00::76 activate            
    maximum-paths 64                      
  exit-address-family                     
  neighbor FC00::7A remote-as 64600       
  neighbor FC00::7A description ARISTA03T1
  neighbor FC00::7A allowas-in 1          
  address-family ipv6                     
    neighbor FC00::7A activate            
    maximum-paths 64                      
  exit-address-family                     
  neighbor FC00::7E remote-as 64600       
  neighbor FC00::7E description ARISTA04T1
  neighbor FC00::7E allowas-in 1          
  address-family ipv6                     
    neighbor FC00::7E activate            
    maximum-paths 64                      
  exit-address-family                     

root@str-s6000-acs-7:/etc/quagga# vtysh -c "show ipv6 bgp " | grep "20c0:a940"
root@str-s6000-acs-7:/etc/quagga#

ARISTA01T1#show ipv6 bgp neighbo fc00::71 advertised-routes | grep a940                      
 * >    20c0:a940::/64      fc00::72         -       -       -      64600 65534 64605 65100 ?
 * >    20c0:a940:0:40::/64 fc00::72         -       -       -      64600 65534 64605 65100 ?

[lguohan]

addressed in sonic-net/sonic-buildimage#741